Method of manufacturing friction facing and like materials



Patented on. so, 1945 METHOD OF MANUFACTURING FRICTION FACING AND LIKEMATERIALS Maurice Sall, New York, N. Y., asslgnor'to tion of DelawareThermoid Company, Trenton, N. J., a corpora- No Drawing. ApplicationFebruary 24, 1941, Serial No. 380,397

1 Claim. (Cl. 92-55) This invention relates to the manufacture offriction and like materials, and a principal object of the invention isto provide an improved method of manufacture capable of yielding amaterial of improved characteristics on an economically favorableproduction basis.

The rapid development of transport industries entailing the use ofheavier vehicles operating at higher speeds imposes an increasingrespnsibllv ity on the friction materialsused in the braking systems.The factors of industrial competition and mass production, however,substantially preclude an advance in the cost of friction materialscommensurate with the advance in quality, and it is necessary,therefore, that quality advances In proceeding in accordance with theinvention,

I may employ the ingredients commonly used in the manufacture offriction materials, which basically are as follows:

vAsbestos fibre Organic fibre Inert filling materials Metal chips orpowders Home suitable bonding agent, preferably of the thermosettingplastic type.

These ingredients are first compounded, on a ball mill, for example, orby other suitable means, in a manner preferably to thoroughly open outthe asbestos fibres and to intermix them with the organic fibres with ahigh degree. of uniformity. The inert filling materials, metal chips orpowders, and the bonding material are in this operation broken up tofine condition and evenly distributed throughout the fibre mass.

This compound is then suspended in water to form a slurry of fairfluidity, such a slurry being obtainable by addition of say eight partsby weight of water to one part of the compound. It

has been found that the relative distribution of j the various elementsor ingredients in the coma shall be obtained primarily through improveddrainage has been completed, or has reached an advanced stage, highvacuum is applied under the filter and is maintained until all thewater, excent a certain amount not susceptible to removal by thismethod, is withdrawn. Instead of the high vacuum for removal of themajor portion of the residual water, pressure may be used, in which casethe said water is expressed from the mass; or pressure and vacuum may beused in conjunction to obtain the desired effect.

In the initial drainage by gravitation, the slow running out of theexcess water from the mass has a tendency to orient the fibres in amanner facilitating the now of fiuid through the mass, but the movementof the excess water in'this step is insufficiently energetic to disturbthe distribu-,

tion throughout the fibres either of the filling materials, the metalparticles, or the bonding plastic.

Nor is the aforesaid orienting tendency sufliciently great to effect acomplete orientation of the fibres in one direction, but on the otherhand has the effect of correcting any such orientation that may haveoccurred when the slurry is fed to the filter. In the deposited fibrousmass left after drainage is finished, therefore, there is asifbstantially complete absence of definite orientation, the fibresextending in all directions and being distributed and interlaced in amanner calculated to afford a highly homogeneous body displaying greatstrength in all directions and high resistance to rupture.

After gravity. drainage is completed, the high vacuum or pressure, orboth, is imposed upon the filter as described,,and a shock effect isthereby produced which causes the fibres to jam themselves together intoa highly homogeneous mass which, nevertheless, presents no unduly highresistance to fluid flow therethrough, so that the forced drainage iseffective to remove a major percentage, say in the neighborhood of 70%,of the water originally employed in making up the slurry.

pound remains substantialy unchanged in the slurry. This slurry is thenpoured onto suitable filter frames and the excess water permitted todrain out by gravitation.

The sheet remaining after forced drainage, al-' though including nodirect bonding material effective in the cold, is yet sufficiently solidto permit handling without exercise of any extraordinary precautionsagainst breaking or tearing. This solidity results from the thoroughinterfelting of the fibres in the sheet, which in its turn results fromthe pretreatment given the fibres in the initial compounding operation,in the gravity drainage, and subsequently in the high vacuum and/orpressure drainage. The sheet may now be placed between wire or othersuitable screens and ft t gravity cold-pressed under a pressure of,preferably, at

,or to finally set the bonding plastic.

least'300 pounds per square inch of the surface area, the purpose ofthis pressure being to squeeze out as much as possible of the remainingwater. The higher the pressure used in this operation, the better,although preferably the pressure should not .materially exceed 1000pounds .per square inch. After the cold-pressing operation, thereordinarily remains in the neighborhood of 8% to 10% of water in thesheets over and above the water content of a normally dry sheet whichmust be removed by drying, and for this drying operation any temperaturemay be used below that required to polymerize or finally set the bondingplastic.

After drying, the sheets are placed either in molds or frames andhot-pressed at a temperature and for a period of time necessary topolymerize The pressure used in this operation should be sufficient toobtain maximum density and homogeneity of the finally resulting frictionmaterial, and should, therefore, be at least 1600 pounds per square inchof the efiective molding area.

A further advantage of the method of manufacture described above is thatit permits the production of composite sheets in which, for example, theefiective frictional surface portion may contain all the ingredientsrequired to afford the desired friction characteristics, whereas thesupporting body of the sheet is made of a less expensive compound havingsufilcient solidity to hold the friction facing in place. This resultmay be obtained by first pouring the high-friction-compound slurry ontothe filter frames and allowing it to drain by gravity as fully as thisdrainage method will permit and as described above. A relatively cheapbody-mix slurry is then poured gently over the gravity drainedhigh-friction-mix, and further gravity drainage of both compounds ispermitted to proceed to its final point. High vacuum and/or pressure isthen applied and all the operations proceeded with as preyicusly described.

This method of superimposing one compound upon ariother after gravitydrainage of the first insures complete cohesion between the twocompounds. The method also makes possible the interposin between thesaid facing and backing sections, or anywhere within the mass of theformed sheet, of various reinforcing means, such, for example, astextile fabrics, wire screens and the like.

It will be apparent that a. practice of the aforedescribed inventiondoes not depend on the use of particular ingredients. The nature of thefibres, of the fillers and frictioning elements, and of the bondingagent may vary widely. ,While for the latter thermosetting plastics arepreferred, it is possible to use a wide variety of bonding agents eitherof thermosetting or thermoplastic character, and the pressures andtemperatures employed will vary according to the nature of the saidagent and the characteristics required in the finished product. i

It will be apparent, also, that by the aforedescribed method, thefriction material may be made directly to the thickness and shaperequired in the finished friction element, such, for example, as a.brake lining or clutch facing; or the material may be produced in sheetsof required thickness and the individual friction elements dyed orotherwise cut from this sheet as a blank.

I claim:

The method of manufacturing friction facing and like materials of theclass compounded of fibres, solid particles of a frictioning or otheragent and a normally non-cementitious heat-reactive binding substance,said method comprising first compounding said ingredients in dry stateto the form of a substantially uniformly disseminated mix, suspendingsaid mix in water to form a, fiowable slurry in which the uniformdissemination of the ingredients is substantially preserved, fiowingsaid slurry onto a filter bed and filtering the water through said bedby gravity to form an interfelted fibrous mass in which the fibresextend in all directions, thereafter applying heavy suction to saidfilter with consequent withdrawal of further water from the interfeltedmass, subjecting said mass in the cold to pressure expressing stillfurther moisture, drying the compressed mass at low temperature withoutmaterially affecting the said binding substance, and subsequentlyapplying heavy pressure and heat to the mass to density the latter andto convert the binding substance to cementitious state.

MAURICE SALLE.

